In recent years, endoscopes have been widely used in medical as well as industrial applications. For medical applications, a capsule endoscope has been proposed which greatly reduces the pain associated with obtaining images of internal body parts. Instead of the endoscope including an optical probe having an insertion part, the endoscope is miniaturized and contained within a capsule that is swallowed by a patient. The capsule then radio transmits images as it passes through the body to a receiver located outside the body. One example of such a capsule endoscope is Japanese Laid-Open Patent Application 2001-91860.
In this conventional example, an objective lens and an illumination means formed of light emitting elements which are symmetrically located on opposite sides of the objective lens, are incorporated inside a roughly hemispherical transparent dome. An object is illuminated by the light emitting elements, and reflected light is then imaged onto an image sensor using an objective optical system. Further, the objective lens is fixed relative to the interior of the roughly hemispherical transparent dome as follows. After a barrel for the objective lens is moved with respect to the exposed image sensor so that focusing adjustment is performed, the objective lens is fixed to the lens holding cylinder of the barrel with a fixing screw. Consequently, dust or shaved particles of the lens frame that may be generated upon focusing, may cling to the front surface of the image sensor. Therefore, there has been an instance in which this has prevented a proper image from being obtained. Also, it is possible that such dust or shaved particles may damage the image sensor. Furthermore, where a transparent cover for the purpose of protecting the image sensor has been installed, there has been an instance where dust clings to a surface of the transparent cover and causes a portion of the image to be obscured.
In addition, in the above-mentioned design, the image sensor and the objective lens are positioned via multiple members. Due to the manufacturing and assembly tolerance of each member being finite, this increases the likelihood that an optical parameter of importance, such as angle of view or depth of field, will be incorrect due to the integration of tolerances of many components.